1. Field of the Invention
The present invention relates generally to optical fiber, and particularly to graded index multimode fibers.
2. Technical Background
The bandwidth of multimode fibers (MMF) is limited mostly by inter-modal chromatic dispersion. To minimize the inter-modal chromatic dispersion, MMF are designed with graded index α-profiles. For optimum bandwidth, the parameter α is about 2. However the optimized α value depends on wavelength due to the material dispersion. Because the bandwidth is very sensitive to profile change from its optimum shape, the operating window with high bandwidth is very narrow.
The bandwidth can be increased with multiple dopants. Known fibers utilize co-doping of germanium and boron. However, boron increases fiber attenuation, increasing the transmission losses of the MMF. Other known multimode fibers have at least one dopant which has lower concentration in the fiber axis than concentration in the region of light guiding core.